Aluminum dipsticks are frequently used to measure the contents of underground storage tanks by insertion of a dipstick down a fill tube, retraction, and observation of the position of the boundary between wet and dry portions of the dipstick. Comparison of daily readings with the metered pumpage gives an indication of the presence of leaks. Careless operators may drop a dipstick down a fill tube and damage the bottom wall of the tank. For tanks made of glass fiber reinforced plastic, prior attempts to prevent damage from dipsticks have included installing steel plates at the bottom of the tank beneath the fill tube, or pouring rubberized epoxy resin down the fill tube.
Because contractors frequently install the fill tube in other than the intended fitting, some companies order metal plates under all fittings at the time an order is placed for a tank. The different plate specifications render it difficult to maintain a line of standard tanks.